1. Field of the Invention
The present invention relates to an organic light emitting display (OLED) device and method for fabricating the same and, more particularly, to an OLED device having anode layers with a reflective layer interposed therebetween and method for fabricating the same.
2. Discussion of the Background
Generally, an OLED device is an emissive display device that emits light by electrically exciting fluorescent organic compounds. An OLED device may be considered a passive matrix OLED (PMOLED) device or an active matrix OLED (AMOLED) device depending on a manner of driving N×M pixels, which may be arranged in a matrix. The AMOLED device is suitable for large displays because of its low power consumption and high resolution, as compared to the PMOLED device.
Depending on a direction which light emits from the organic compound, an OLED device may be a top-emitting OLED device, a bottom-emitting OLED device, or a top and bottom-emitting OLED device. The top-emitting OLED device emits light in an opposite direction of a substrate with the pixels positioned thereon and it may have a high aperture ratio, unlike the bottom-emitting OLED.
Demand is increasing for an OLED device comprising both a top-emitting type, for a primary display window, and a bottom-emitting type, for a secondary display window, because the device may be miniaturized and it may consume little power. Such an OLED device may be primarily used for a portable telephone including the secondary display window outside and the primary display window therein. The secondary display window consumes less power than the primary display window, and it may remain on when the portable telephone is in a call waiting state, thus allowing a reception state, battery remaining amount, time, and the like to be observed at any time.
FIG. 1A is a cross-sectional view showing a conventional OLED device.
First, a buffer layer 110 is formed to a predetermined thickness on a transparent insulating substrate 100, and a thin film transistor, which includes a polycrystalline silicon pattern 122, a gate electrode 132, and source and drain electrodes 150 and 152, is formed on the substrate. Source and drain regions 120, having implanted impurities, are formed at both sides of the polycrystalline silicon pattern 122. A gate insulating layer 130 is formed on the entire surface of the substrate including the polycrystalline silicon pattern 122. The source and drain electrodes 150 and 152 are formed on an interlayer insulating layer 140, and they are connected to the source and drain regions 120 through contact holes.
A passivation layer 160 is then formed to a predetermined thickness on the entire surface and etched by photolithography and etching processes to form a first via contact hole (not shown) exposing either the source or drain electrode 150 or 152. FIG. 1A shows the exposed drain electrode 152. The passivation layer 160 is an inorganic insulating layer, which may comprise a silicon nitride layer, a silicon oxide layer, or a stacked structure thereof.
Next, a first insulating layer 170 is formed on the entire surface of the substrate. It may be formed of one material selected from a group consisting of polyimide, benzocyclobutene series resin, spin on glass (SOG), and acrylate. The first insulating layer 170 is formed to planarize a pixel region.
The first insulating layer 170 is subsequently etched by photolithography and etching processes to form a second via contact hole (not shown) exposing the first via contact hole.
Next, a stacked structure of a reflective layer (not shown) and a thin layer (not shown) for an anode is formed on the entire surface. The reflective layer may be formed of a metal having high reflectivity, such as aluminum (Al), molybdenum (Mo), titanium (Ti), gold (Au), silver (Ag), palladium (Pd), an alloy of these metals, or the like. Forming the reflective layer described above provides a top-emitting OLED device. On the other hand, forming the reflective layer in a subsequent process provides a bottom-emitting OLED device.
The thin layer for the anode is formed about 10 to 300 Å thick using a transparent metal material, such as Indium Tin Oxide (ITO).
The stacked structure is subsequently etched by photolithography and etching processes to form an anode 182 and a reflective layer pattern 180a. 
A second insulating layer pattern 190 defining a emission region may then be formed on the entire surface of the substrate. The second insulating layer pattern 190 may be formed of one material selected from the group consisting of polyimide, benzocyclobutene series resin, phenol resin, and acrylate.
Subsequently, an emission layer 192 is formed in the emission region defined by the second insulating layer pattern 190, using a small molecule deposition method or a laser induced thermal imaging method. A cathode (not shown) and the like are then formed to thereby complete the OLED device. When forming a top-emitting OLED device, the cathode is formed of a transparent electrode or a transparent metal electrode, and when forming a bottom-emitting OLED device, the cathode is formed of a metal electrode having a reflective layer, or a reflective electrode.
If the reflective layer pattern and the anode in the top-emitting OLED device are formed in the stacked structure as described above, they may be simultaneously exposed to an electrolyte solution that is used in the photolithography and etching processes, which may damage the anode. Such damage may degrade the device's optical properties, such as brightness.
FIG. 1B is a cross-sectional view showing another conventional OLED device. The OLED device of FIG. 1B may form a reflective layer pattern 180b in an island structure to solve the above problem. This may prevent the reflective layer pattern 180b and the anode 182 from being simultaneously exposed to the electrolyte solution.
Since the top-emitting OLED device uses a resonance effect of light as described above, forming the anode as thin as possible facilitates color-coordinates adjustment. However, forming the thin anode may cause a short circuit at a step of the via contact hole. Further, when fabricating the OLED device including both the top-emitting OLED device and the bottom-emitting OLED device, using equally thick anodes for the top and bottom-emitting OLED devices may degrade the device's optical properties due to an increase in resistance.